[MRCA] T-195 Auto-NoTune

Wed Jul 15 10:38:49 EDT 2015

The weight, crazy high current requirements and AM only operation of the T-195, An/GRC-19 makes me appreciate running an AN/GRC-106 all the better! It is interesting to see that on a more modern transmitter they dropped the automatic Tune and Load system and opted for a manual system that still is biased around the idea of DC balance discriminators like the ARC-38, T-195 or 618T but decided to dispense with the auto tune motors. Not to say the 106 does not have issues with servo systems if you're using the whip antenna but with using the 50 Ohm system everything is fairly stable and works surprisingly well. Also the 106 only draws around two amps in receive only, about five amps in transmit standby and around thirty or so amps in full power transmit. Think a GRC-19 set up may draw more than that just in standby.
A note about the little Collins choppers, as Mr. Smith says you are way better off removing power from the servo systems unless needed because those little choppers are getting harder to come by and many that are around or that you may have on the shelf go bad over the years.

Ray F

From: MRCA [mailto:mrca-bounces at mailman.qth.net] On Behalf Of B. Smith
Sent: Wednesday, July 15, 2015 10:23 AM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] T-195 Auto-NoTune

I gave up on the dynamotor power supply for my T-195 years ago. Built up my "junk box" supply  in sections.  On the left is the HV and 400 cycle supply. On the right are the Bias and Screen supplies. I cheated a little bit on the Bias supply and used a small Lambda supply picked up at a ham fest. 28 Volts is supplied by the Operations Center  DC  buss and everything is metered including bias with the exception of the  400 cycle line (I did not have any 400 cycle AC meters) The 400 cycle line does have a neon indicating light on the front panel . Building the supplies in sections allow for easier maintenance and gives your back a break.  Note that the HV supply is on small wheels.   :-)  Once the set is tuned to frequency  I turn OFF the 400 cycle supply to keep the servos from hunting  and sitting around making that little dithering noise.  4 wires to the T-195 with a 24 volt control relay installed in the HV section.   See attch photo.
Z

[cid:image001.jpg at 01D0BEEA.6EDC9940]

On 7/15/2015 6:46 AM, DSP3 wrote:
Corollary to the current discussion, I've been thinking (dangerous activity!) about building an external  KV DC supply for the T-195( ) transmitters.  The original dynamotor requires about 68 amps of inrush current.  The running current is maybe 35-40 amps, key down.  The HV dynamotor is the killer for the PP-4763 and the 7333.  Also poor old K2 takes beating in the straight T-195.  I figure one would need 4 wires for the interconnect; ground, "start", control, and B+.  The T-195B (with the Victoreen solid-state supply) requires a straight 32 amps to start and run.  Now, the rotary unit that makes the 400 Hz voltage would have to stay, of course as it produces multiple voltages.  Some units are mobile, of course, but many are at home and permanently ensconced.  A hidden power supply might be an idea and DC  current might be reduced to as low as maybe 20 amps, total?   Any interest?

Jeep - K3HVG

On 7/15/2015 6:31 AM, DSP3 wrote:
Chris,

But that I was the guru for the GRC-19, but that's not the case, of course.  An area of concern for the servo system are the matched sets of discriminator diodes.  The manual admonishes to change these diodes on a VERY regular basis, something like every 60 hours of use!. To even mention those specific components is a clue.  I think the requirement for a higher DC bus voltage is not a design issue but one where other components in the servo loop are deteriorating.  I'd, of course, check the tubes in the servo chain and then replace the diodes.  The a.c. chopper could also be going bad.  Its the same part as in the ARC-38.  They're available and not too expensive, either.  The last time I found them, they were about $20 each.  I may still have one or two here and someone on the group will surely have some.

Jeep - K3HVG

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